The invention relates generally to disk brake assemblies and, more specifically, to the control of disk brakes via magnetic field sensors and magnetically encoded disk brake rotors.
Many modern vehicles incorporate at least an Anti-skid Braking System (ABS) and/or a Traction Control (TC) system to aid in the prevention of wheel lock-up or wheel slip. When driving surface conditions are less than optimal (for example, in snow, rain, or mud), wheel lock-up during braking and wheel slip during acceleration can cause a reduction in control of the vehicle between the driving surface and the wheels. It is the purpose of the ABS and TC systems to minimize any such reductions in control of the vehicle.
Typically, the ABS and/or TC systems rely upon wheel speed sensors mounted on a stationary part of the vehicle near the rotating wheels or brake rotors. Feedback signals from these speed sensors are sent to a controller within the vehicle, which monitors the feedback signals received from the various speed sensors and determines if wheel lock-up or wheel slip is occurring. Such a determination is usually made by comparing a reference speed signal (e.g., the average speed of all wheels at a particular moment) with a sensed speed signal at a particular wheel. If an abrupt change in the absolute value of the difference of the reference speed signal and the sensed speed signal exceeds a predetermined threshold, a signal is issued to a controller to indicate that wheel lock-up or wheel slip is occurring. In the case of the detection of wheel lock-up, the vehicle's disk brake at the offending wheel is momentarily disengaged in an effort to reduce skidding of the vehicle. In the case of the detection of wheel slip, the vehicles disk brake at the offending wheel may be momentarily engaged in an effort to reduce wheel spin.
The speed sensors used in conventional ABS and TC systems often rely on a physical pattern in the rotating surface, such as a toothed notch in the brake rotor or the wheel itself, to enable determination of wheel lock-up or wheel slip. Conventional sensors such as Hall sensors, variable reluctance sensors, and even optical sensors use the physical pattern in the rotating surface to aid in the determination of the rotational speed of the wheel. From the rotational speed, the ABS or TC systems can determine if a particular wheel is locked or slipping, as discussed above. However, due to the harsh environments to which the wheel assemblies are exposed, it is not uncommon for the physical pattern (often a toothed notch) to become clogged with debris or rust, reducing or eliminating the detection performance of the speed sensors by the ABS or TC system. Thus, performance of the overall ABS and/or TC systems may be affected.
Additionally, the speed sensors used in conventional ABS and TC systems have a relatively low bandwidth. Thus, the bandwidth of the corrective action, such as a momentarily release the brakes to reduce skidding or a momentarily application of the brakes to reduce wheel spin, is correspondingly low. This low bandwidth reduces the effectiveness and response time of the ABS and TC systems.
Due to the harsh environmental conditions to which most ABS and/or TC systems are exposed, conventional ABS and/or TC systems are prone to failure, necessitating costly repairs or replacement. Furthermore, the low bandwidth of the speed sensors of conventional ABS and/or TC systems also limits the effectiveness of the systems in situations where reaction time is paramount. Without a functioning ABS and/or TC system, a vehicle will obviously lack an effective remedy to unexpected wheel lock-up or wheel slip.
Therefore, it is desirable to provide a disk brake system that does not rely upon surface patterns on a wheel or disk brake rotor or conventional speed sensors to provide feedback for an ABS and/or TC system. Utilization of such a system will greatly improve the lifespan and effectiveness of ABS and/or TC systems.